The objective of this project is to increase our understanding of the genetic basis of cellular differentiation. The in vitro differentiation of Drosophila neurons and myocytes, from their respective blast cells, is the experimental system on which genetic and developmental analysis is being performed. In addition to two known mutants (supplied by T. Wright and J.D. Mohler), we have induced 29 recessive embryonic lethals or maternal lethals which affect neuron and/or myocyte differentiation in vitro. EMS and ICR-170 are being employed as mutagens. The 31 mutations are distributed among the three major chromosomes; 5 on the X, 15 on the second and 11 on the third chromosome. Complementation and recombinational analysis is in progress. Through the analysis of mutants which affect neuron and/or myocyte differentiation, we propose to piece together the gene directed steps (unique and common) in the differentiative pathway. BIBLIOGRAPHIC REFERENCES: Donady, J. James 1974. Maternal effect lethality associated with a compound XY chromosome. Genetics 77:s18. Donady, J. James and Eric Fryberg 1975. A method of Culturing Drosophila Embryonic Cells in vitro for nerve and Muscle Differentiation. In Tissue Culture Association Manual (V. Evans, V. Perry and M. Vincent editors), (in press).